[H-3] DOPAMINE UPTAKE BY PLATELET STORAGE GRANULES IN PARKINSONS-DISEASE

[H-3] Dopamine (DA) uptake by platelet storage granules was determined in 10 never-treated patients with Parkinson's disease (PD) (in 6 of t hem, also after 6 months of levodopa treatment), in 18 long-term levod opa-treated patients and in 15 age-matched normal controls. maximum ve locity (Vmax) of DA uptake was significantly lower in the group of nev er-treated PD subjects compared to healthy controls (P<0.001) and also lower compared to the PD long-term treated patients (P<0.025). The Vm ax of PD never-treated changed after submitting the patients to 6 mont hs treatment (P<0.025) and became similar to the Vmax in the treated g roup. The apparent Michaelis constant (Km) of DA uptake in PD never-tr eated was also significantly different from controls (P<0.005) and als o different (but not significantly) from PD ''long-term'' treated pati ents. Decreased DA uptake by platelet storage granules in PD may refle ct a generalized defect of dopaminergic cells with an impairment in th e vesicularization of DA which may contribute to the symptomatology of this motor disease.